Download Balancing Chemical Equations Guide

Balancing Chemical Equations
An equation is balanced when there are an equal number of atoms on each side
of the equation.
Why? CONSERVATION OF MASS
Matter is neither created nor destroyed!
Example of a balance equation: 2H2 + O2 → 2H2O
Notice here are two types of numbers in this equation
1. Subscripts: example - O2
The subscript is the number after an atom and can NEVER be changed when
balancing equations.
2. Coefficients: example 2H
A coefficient is the number in front of the atom or compound that can be changed
to balance the equation.
If there is no coefficient assume the number 1. There is one molecule or mole of
O2 in the above equation. For that same oxygen gas(O2) there are 2 atoms of O .
In order to calculate the numbers of atoms multiply the subscript by the
coefficient for each atom in the molecule.
For example: to calculate the atoms in H2O on the product side in the above
equation we must multiply the coefficient by the subscript.
When we do this we get we get 4 H atoms and 2 O atoms. This equals the 4H
atoms and 2O atoms on the reactant side.
2Ca(NO3)2
The one above is more complicated. Remember to multiply the coefficient by the
subscript of each atom. If there is no subscript it is assumed 1. If there are
brackets the subscript is for every atom within the bracket.
So, in the above compound with a subscript of 2, there are 2 Ca atoms. 4 N
atoms (2 atoms due to the subscript outside the brackets times the coefficient of
2) and 12 O atoms (6 due to the subscript in and out of the brackets times the
coefficient of 2).
Steps to Balance Equations
1. If the equation is not written for you, write the reactants on the left followed by
the products on the right.
2. Use a chart to help balance the equation. Write each atom on each side with
the number of atoms next to it. One side is for the reactants; the other side is for
the products. Keep the atoms in the same order on the reactant and product
side.
ZnCl2 + (NH4)2S → ZnS + NH4Cl
Zn
Cl
N
H
S
1
2
2
8
1
Zn
Cl
N
H
S
1
1
1
4
1
3. Balance one atom at a time. Change your numbers in the chart for every atom
that may have changed. Here I started with Cl. I have 2 Cl on the reactant side,
so I need 2 Cl on the product side. This changed H and N so I have to change
this in my inventory for each atom before moving on.
ZnCl2 + (NH4)2S → ZnS + 2NH4Cl
Zn
Cl
N
H
S
1
2
2
8
1
Zn
Cl
N
H
S
1
1 2
1 2
4 8
1
6. Now we are balanced. We have equal number of atoms on the reactant side
and product side of the equation.
2ZnCl2 + (NH4)2S → ZnS + 2NH4Cl
8. Finally make sure the coefficients are in the lowest whole number ratio.
The above coefficients are 2, 1, 1, 2 this is the lowest whole number ratio for
each coefficient.
Super fun!! Now go and practice.